yes, you can use them for other equipment
EQ: equalization happens somewhere for both tape and lp. these are labeled tape, or record: but there is no eq involved in the preamp ’tape loop’ itself: the tape eq or any processing happens elsewhere.
OUT: they are line level, same as pre-out, send line level out to something
IN: use for any line level source in.
LISTENING: vintage, or new: various ’monitoring’ schemes/switches exist, make sure you know what you have or will have, how it works.
SIGNAL STRENGTH (in round numbers):
check the ’line’ specs of your unit(s). old days, pre-amps didn’t exist. amps were designed for A LINE LEVEL OF 1 volt in. pre-amps came about to boost new magnetic tape head’s and NEW magnetic cartridge’s weaker signal strength up to the 1 volt needed by existing AMPS. later: even smaller signal strength from low output MC cartridges need a pre-pre amp.